This invention is directed to the production of six types of inorganic crystalline fibers:
(1) fibers wherein a fluormica constitutes the predominant crystal phase; PA1 (2) fibers wherein a fluoramphibole constitutes the predominant crystal phase; PA1 (3) fibers wherein canasite constitutes the predominant crystal phase; PA1 (4) fibers wherein potassium and/or sodium fluorrichterite constitutes the predominant crystal phase; PA1 (5) fibers wherein fluorapatite constitutes the predominant crystal phase; and PA1 (6) fibers wherein a fluoride-containing, spodumene-type crystal constitutes the predominant crystal phase. PA1 (A) batches are melted, the melt cooled to a temperature below the transformation range thereof and simultaneously shaped into a body of a desired geometry, and the body heated in a closed container at a temperature within the range of about 800.degree.-1000.degree. C. for a period of time sufficient to grow fibers projecting from the surface of the body; PA1 (B) batches free from MoO.sub.3 and/or WO.sub.3 and/or As.sub.2 O.sub.3 are melted, the melt cooled to a temperature below the transformation range thereof and simultaneously shaped into a body of a desired geometry, the body comminuted to finely-divided particles, the particles mixed with finely-divided particles of MoO.sub.3 and/or WO.sub.3 and/or As.sub.2 O.sub.3, and that mixture heated in a closed container at a temperature within the range of about 800.degree.-1000.degree. C. for a period of time sufficient to grow fibers projecting from the surface of the particles; and PA1 (C) batch materials in finely-divided particulate form corresponding to or closely approximating the stoichiometry of the desired crystalline fibers and including appropriate amounts of MoO.sub.3 and/or WO.sub.3 and/or As.sub.2 O.sub.3 and fluoride are mixed together, that mixture is formed into a body of a desired configuration, and that body is fired in a closed container at about 800.degree.-1000.degree. C. for a period of time sufficient to grow fibers projecting from the surface of the body.
The production of inorganic crystalline articles containing a fluormica as the predominant crystal phase has been the subject of numerous disclosures. To illustrate:
U.S. Pat. No. 3,689,293 describes the preparation of such articles from precursor glass compositions in the R.sub.2 O-MgO-(Al.sub.2 O.sub.3,B.sub.2 O.sub.3)-SiO.sub.2 -F system, wherein R.sub.2 O is an alkali metal oxide. X-ray diffraction analyses identified the basic mica as corresponding to a fluorophlogopite solid solution; that solid solution commonly comprising three components: normal fluorophlogopite, KMg.sub.3 AlSi.sub.3 O.sub.10 F.sub.2, boron fluorophlogopite, KMg.sub.3 BSi.sub.3 O.sub.10 F.sub.2, and a subpotassic aluminous phlogopite whose extract composition was unknown but which was thought to approach close to K.sub.0.8 Mg.sub.2.9 Al.sub.0.9 Si.sub.3.1 O.sub.10 F.sub.2.
U.S. Pat. No. 3,732,087 is drawn to articles wherein tetrasilicic fluormica crystals constitute the predominant crystal phase. Such articles are prepared by heat treating precursor glass articles having compositions within the (K,Rb,Cs).sub.2 O-(Sr,Ba,Cd)O-MgO-SiO.sub.2 -F system.
U.S. Pat. No. 3,756,838 is directed to articles wherein an alkali metal-free, alkaline earth metal fluormica constitutes the predominant crystal phase. Such articles are produced by heat treating parent glass articles having compositions in the (Ba,Sr)O-MgO-Al.sub.2 O.sub.3 -SiO.sub.2 -F field.
The formation of inorganic crystalline articles wherein fluoramphibole crystals comprise the predominant crystal phase is disclosed in U.S. Pat. No. 3,839,056. Such articles are prepared by heat treating precursor glass articles having compositions within the (Li,Na).sub.2 O-(Ca,Mg)O-(Ca,Mg)O-(B,Al).sub.2 O.sub.3 -SiO.sub.2 -F system. The backbone of the amphibole structure is formed by double silicate chains which are crosslinked alternately by oxygen and fluorine. Each double chain is made up of single chains arranged side-by-side in a herringbone pattern. Fluoramphibole crystals can have a fibrous or needle-like habit. The growth of such crystals in situ in glass articles can yield a fiber-containing matrix wherein the fibers are undamaged and, therefore, extremely strong. X-ray diffraction studies evidenced three different types of fluoramphibole crystal structures; viz., fluorrichterite, Na.sub.2 CaMg.sub.5 Si.sub.8 O.sub.22 F.sub.2, fluormagnesiorichterite, Na.sub.2 Mg.sub.6 Si.sub.8 O.sub.22 F.sub.2, and lithium-containing proto-amphibole, LiMg.sub.6.5 Si.sub.8 O.sub.22 F.sub.2.
The production of inorganic crystalline articles containing canasite as the predominant crystal phase is described in U.S. Pat. No. 4,386,162. The crystals grown in situ through the heat treatment of parent glass bodies are conjectured as having the formula Ca.sub.5 Na.sub.4 K.sub.2 [Si.sub.12 O.sub.30 ]F.sub.4 with probable solid solution to Ca.sub.5 Na.sub.3 K.sub.3 [Si.sub.12 O.sub.30 ]F.sub.4. As is explained there, canasite consists of a multiple chain silicate demonstrating an anisotropic blade-like crystal habit. Electron microscopy and x-ray diffraction studies have indicated that, structurally, canasite crystals are composed of parallel silicate chains crosslinked to make a long, box-like backbone in which the potassium ions rest. Those complex chain units are crosslinked into groups of four and are separated by networks composed primarily of Na(O,F).sub.6 and Ca(O,F).sub.6 octahedra. That characteristic interlocking chain silicate structure has yielded articles exhibiting moduli of rupture in excess of 50,000 psi and exceptional toughness, i.e., resistance to impact.
Inorganic crystalline articles containing potassium fluorrichterite as the predominant crystal phase are disclosed in U.S. Pat. No. 4,467,039. Potassium ions are substituted in part for sodium ions in the fluorrichterite structure, resulting in crystals having the formula KNaCaMg.sub.5 Si.sub.8 O.sub.22 F.sub.2. The habit of those crystals is strongly anisotropic and predominantly unidimensional. Fundamentally, the crystals consist of polymer chain silicates in which double or higher order multiple chains form the backbone.
Because the substance of animal and human bones consists essentially of hydroxyapatite, Ca.sub.5 OH(PO.sub.4).sub.3, which is permeated in an intimate mixture of albuminoids (collagen), considerable research has been undertaken to synthesize the mineral hydroxyapatite and its fluoride-containing analog, Ca.sub.5 F(PO.sub.4).sub.3, for use as bone implant and bone replacement materials. U.S. Pat. Nos. 3,922,155, 4,120,730, and 4,131,597 are illustrative of the research which has been directed to the production of glass-ceramic materials containing fluorapatite at the predominant crystal phase.
Inorganic crystalline articles containing spodumene (classic formula Li.sub.2 O:Al.sub.2 O.sub.3 :4SiO.sub.2) as the predominant crystal phase have been extensively marketed, principally because of their low coefficient of thermal expansion and their relatively high refractoriness. Such articles were first described in U.S. Pat. No. 2,920,971, and have been the subject of numerous subsequent patents.